ABSTRACT This proposal is aimed at testing the contribution of the Rho GTPases Rac1 and RhoB in the dorsal striatum to the mechanisms underlying alcohol use disorder (AUD). Rac1 and RhoB play an important role in cytoskeleton rearrangement as well as in the remodeling of dendrites and spines. We recently discovered that excessive alcohol intake and withdrawal activate Rac1 and RhoB in the mouse dorsomedial striatum (DMS), and dorsolateral striatum (DLS), respectively. Based on published and preliminary data, we will test the hypothesis that alcohol activates Rac1 and RhoB, in DMS and DLS neurons, respectively, leading to cellular adaptations which in turn drive the development and/or maintenance of alcohol drinking behaviors including goal directed and habitual alcohol seeking. This hypothesis will be explored by the following aims. Aim 1 will determine the mechanism by which heavy alcohol use actives Rac1 and RhoB in the DMS and DLS. We will also determine whether the small G proteins are activated in subpopulation of striatal neurons. Aim 2 will determine the cellular consequences of Rac1 and RhoB activation in the DMS and DLS, respectively. Specifically, will examine the hypothesis that Rac1 activation by alcohol in the DMS promotes F-Actin formation and dendritic tree branching as well as spine maturation. We will also test the hypothesis that alcohol-dependent RhoB activation in the DLS leads to opposite outcomes e.g. dendritic tree shrinkage and increase in the number of immature spines. Aim 3 will address the behavioral consequences of Rac1 and RhoB activation in the DMS and DLS, and determine whether the small G proteins contribute to the development and/or maintenance of alcohol drinking behaviors. Finally, as the DMS and DLS are central regions in circuitries that drive goal directed and habitual behaviors, respectively, we will determine whether Rac1 and RhoB drive goal directed and habitual alcohol seeking. To achieve these goals, we plan to combine state of the art molecular/genetic tools with mouse alcohol drinking paradigms. If successful, data generated from the studies will: a. shed a light on the contribution of an important group of signaling molecules to AUD; b. will enable us to gain insights on how alcohol exposure produces structural modifications in the dorsal striatum; c. will potentially identify the molecular mechanisms underlying goal-directed and/or habitual alcohol seeking; d. as small molecules targeting Rho GTPases are being developed for other indications, the application has a clear translational trajectory.